Perhaps you should read the article, for it offers not only a better explanation of the "dip" in the 40s but for the subsequent increase in satisfaction/content

Perhaps you should read the article, for it offers not only a better explanation of the "dip" in the 40s but for the subsequent increase in satisfaction/contentment/happiness that then lasts until near the very end of life. It's a long article. I have no summary. Other than "period of adjustment to changing values, none of which are related to mortality".